The present invention relates to a novel synthetic antimicrobial which exhibits strong antibacterial activities against Gram-positive, Gram-negative bacteria and anaerobic bacteria.
Quinolone type synthetic antimicrobials have been widely used in the clinical field as an agent having an excellent antibacterial activity. However, compared to Cephalosporin and Penicillin type xcex2-lactam antibiotics, Quinolone type synthetic antimicrobials have problems, for example, that they cause a lot of side effects concerning the central nervous system, that they cause critical side effects such as a spasm inducement, and that bacteria resistant due to such antimicrobials rapidly spread. Therefore, it has been desired that synthetic antibacterial agents be developed which are effective against the bacteria resistant to such an antimicrobial and have fewer side effects and a broad antibacterial spectrum.
In recent years, many studies on Quinolone type antimicrobials have been made since Norfloxacin, a Quinolone type compound including a fluorine at the 6-position, was developed. However, there are not many studies on 4-oxoquinolizine antimicrobials having a 2-pyridone skeleton as a partial structure has been made intensively.
Therefore, the present invention provides a 4-oxoquinolizine antimicrobial having new structure and strong antibacterial activities against Gram-positive, Gram-negative bacteria, and anaerobic bacteria.
The present inventors have conducted extensive research to provide an excellent antimicrobial, and found out that the compounds represented by the following Formula (I) has fewer side effects such as spasm inducement than the conventional antimicrobials and exhibits a strong antibacterial activity. The present invention has been completed on the basis of this finding.
Specifically, the present invention is related to a compound represented by the following Formula (I) or a pharmaceutically acceptable salt thereof: 
wherein
R1 represents a hydrogen atom or a carboxyl-protecting group,
R2 represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a hydroxyl group,
R3 represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a lower alkylthio group, a nitro group, a cyano group, a hydroxyl group or an amino group;
R4 represents a hydrogen atom, an amino-protecting group, an alkyl group or a cycloalkyl group, and
R5 represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkoxy group, an alkylthio group, a hydroxyl group, an imino group or an amino group.